The Insert feature works on selected threads in warp or weft by inserting the threads immediately before the current cursor position and sliding the remaining threads over.
To Insert:
First select the threads that are to be copied and inserted.
Click Copy
Position Cursor to where the threads are to be inserted immediately before.
Click Insert
Keyboard shortcuts: Ctrl+Shift+V | ⇧⌘V
This short video shows using Insert on Warp Threads:
